The present invention relates to bumpers and, more particularly, to bumpers comprised of a rigid rear support frame and a deformable front hollow section with freely extending parallel shanks for embracing the rigid frame.
Bumpers of this kind which may be used for vehicles and also for the protection of stationary objects, e.g. a bumping post arrangement, have become known through Offenlegungsschrift No. 2,360,525, 63c 70 and U.S. Pat. No. 3,638,985. The ends of the two free shank regions shown in these references are placed in ledges that have an approximately hook-shaed cross section and are bolted to the rigid support. This arrangement requires not only an undesirable loss of time during assembly because of the screwing on and tightening of a large number of screws, but also suffers from the disadvantage that the screw bolts are subjected to shearing stress during an impact.
While a bumper construction as per Offenlegungsschrift No. 2,111,309, 63c 70 offers the advantage that both free shank zones of the hollow profile are joined with the rigid support means by hooking or buttoning into it, this is possible only in the case of a front hollow section made of comparatively soft material. Accordingly, this known bumper contains an intermediate layer consisting of a volume-elastic material in the space enclosed by the composite hollow section.
It is the purpose of the present invention to provide a bumper having a deformable hollow front section with free shank regions that embrace a rigid rear support frame, in which the assembly effort can be kept as small as possible without affecting the structural design with respect to the desired energy absorption. The attainment of this purpose in accordance with the invention is characterized in that only one of the free shank regions of the hollow section is connected with the rigid support means by screwed connections, while the other free shank zone is buttoned or hooked into a holding element of the rigid support means. This holding element has an approximately U-shaped cross section. Also, the screw-connected free shank region is provided with a support edge that bears on the front portion of the rigid support means in order to relieve shear stresses on the screw bolt.
Thus, in accordance with the invention only a first one of the free shank regions of the hollow section is maintained on the rigid support means by screwed connections. Also, in order for the screwed connections not to be stressed in a harmful manner during impacts, there is provided in front of the screwed connections a support for the hollow section by the front portion of the rigid support means. In contrast the connection between the other or second free shank region of the hollow profile and the rigid support means is designed as an interlaced or hooked connection. This design preferably provides for the holding element to be formed so as to (1) grip the end of the second free shank region only on the side facing away from the first one of the free shank regions, (2) provide a clearance between the other side of the end and the holding element in order to permit the interlacing and (3) force the second free shank area preceding the holding element to bear against the rigid support means. The bracing of the second free shank region on the rigid support means may be obtained by projections on the rigid support means and the second free shank region, respectively, which are directed towards each other. In one embodiment of the invention the inner surface of the second free shank region, that faces the rigid support means and extends behind the point where the rigid support means braces it, is inclined in cross section relative to the rigid support means.
However, whatever structural means is used for the bracing of the second shank region, it must form a kind of swival axis which makes it possible during assembly to initially introduce the second free shank region into the holding element by utilizing the clearance between the latter and the rigid support means. This must be accomplished without any obstruction by the hook-shaped form of the holding element. After the second free shank region is inserted, the hollow section is swivelled in cross section until the first free shank region assumes a position that permits the screwed connection to be accomplished. Since the hollow section is comprised of a material that is deformable by the impacts to be absorbed, but is not deformable by the forces occurring during assembly, the swivelling of the hollow section by necessity results in a swivelling of the end of the second free shank region, until the hook shape of the holding element grips its end from the rear. The swivelling motion terminates once the hook-like rear grip is accomplished and/or when a portion of the first free shank region bears against the front portion of the rigid support means.
Assembly is rendered easier if the second free shank region, which is hooked together with the holding element, is longer in cross section than the first free shank region. This embodiment of the invention offers the additional advantage that in the event of impact, the second free shank region, which is supported by the holding element, can curve outwardly along its portion from outside the holding element to the reinforcing ribs.
Tests have shown that during a collision, due to this outward arching of the second free shank region and also the curving of the portions of the hollow section adjacent to the free shank regions, the reinforcing ribs, which effect a stiffening of the bumper, are subjected to tensile stress. These tensile stresses are so great that in the region of the edges of the ribs adjacent the rigid support, the ribs are broken off from the outer portions of the hollow section. Rounding of the ribs in the transition zones between the reinforcing ribs and the front hollow section cannot prevent this. In accordance with the invention, however, a remedy for the problem can be achieved by spacing the front edges of the reinforcing ribs from the front portion of the rigid support means by a narrow gap, e.g., on the order of 2 mm, and assuring that the edges of the reinforcing ribs in the proximity of the support edge have rounded clearances. In one execution of the invention, each reinforcing rib is provided with a clearance, that has a depth of about 6 mm and is directly adjacent to the supporting edge, and a large radius cut, that passes into the remaining course of the reinforcing rib and into the support edge, respectively. Thereby, there is imparted to each of the reinforcing ribs a greater ability to expand in that region of the ribs that is especially subjected to tensile stress.
It has been found that the bumper in accordance with the invention can be used on automobiles without any deformation bodies arranged behind it. The rigid support means is then rigidly connected with the vehicle or is a component of the frame or the body of the vehicle itself.